When a transmitter employs SVD-based precoding matrices in a MIMO beamforming scheme, an equivalent received channel seen by a receiver is diagonal. In general, diagonality enhances receiver performance as Inter Stream Interference (ISI) is eliminated and the equivalent received Signal-to-Noise Ratio (SNR) increases.
However, when the channel's condition number, that is, the ratio between the largest and smallest eigenvalues, is high, full channel diagonalization accomplished by the SVD precoding procedure degrades performance because a received data stream associated with the lowest eigenvalue suffers from low SNR.
In many Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards, the effect of channel condition number is emphasized due to different Modulation Coding Schemes (MCS) for each MIMO stream not being permitted; a single MCS must be used for all data streams. When the channel condition number is high, the transmitter's chosen MCS needs to be determined based on the smaller eigenvalue, and as a result data throughput decreases.